Bloodletting

A surgeon letting blood from a woman's arm, an oil painting from the 1700s.

Your body contains about 5 litres of blood. Assuming you’re resting, this is pumped around your body in just one minute. Blood is vital to our survival and excessive blood loss can lead to shock and death. Fortunately, our bodies have developed clotting agents as a way to prevent blood loss.

But in earlier historical periods losing blood was considered to be beneficial to health. This practice was called bloodletting and was the most common procedure performed by surgeons for almost two thousand years. They did it to balance the humours, as a surplus was thought to cause ill health. All four classical elements - fire, earth, water and air - were thought to be present in the blood, and so bloodletting was believed to return the patient to general good health. According to Galen, fevers, apoplexy and headache were a result of too much blood, so the surgeon would tie the arm to make the veins swell, cut the patient and drain out a certain amount of blood, a process which was called ‘breathing a vein’. Excessive bleeding could cause anaemia.

Leeches were also used for bloodletting. Applied to the skin, this type of worm can suck several times its original body weight in blood. The use of leeches in Europe peaked between 1830 and 1850, then fell into decline. This was firstly a result of the invention of ‘mechanical leeches’, and then changes in medical models of the body. Today, leeches are used in surgery to help heal skin grafts and restore blood circulation. Their usefulness is no longer attributed to the amount of blood they can suck out, but to an enzyme in their saliva which helps blood flow freely.